154 lines
4.0 KiB
Diff
154 lines
4.0 KiB
Diff
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Hi,
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The attached patch makes sure that we create smaller object code for
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simple switch statements. We just make sure to flatten the switch
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statement into an if-else chain, basically.
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This fixes a size-regression as compared to gcc-3.4, as can be seen
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below.
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2007-04-15 Bernhard Fischer <..>
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* stmt.c (expand_case): Do not create a complex binary tree when
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optimizing for size but rather use the simple ordered list.
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(emit_case_nodes): do not emit jumps to the default_label when
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optimizing for size.
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Not regtested so far.
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Comments?
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Attached is the test switch.c mentioned below.
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$ for i in 2.95 3.3 3.4 4.0 4.1 4.2.orig-HEAD 4.3.orig-HEAD 4.3-HEAD;do
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gcc-$i -DCHAIN -Os -o switch-CHAIN-$i.o -c switch.c ;done
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$ for i in 2.95 3.3 3.4 4.0 4.1 4.2.orig-HEAD 4.3.orig-HEAD 4.3-HEAD;do
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gcc-$i -UCHAIN -Os -o switch-$i.o -c switch.c ;done
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$ size switch-*.o
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text data bss dec hex filename
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169 0 0 169 a9 switch-2.95.o
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115 0 0 115 73 switch-3.3.o
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103 0 0 103 67 switch-3.4.o
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124 0 0 124 7c switch-4.0.o
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124 0 0 124 7c switch-4.1.o
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124 0 0 124 7c switch-4.2.orig-HEAD.o
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95 0 0 95 5f switch-4.3-HEAD.o
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124 0 0 124 7c switch-4.3.orig-HEAD.o
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166 0 0 166 a6 switch-CHAIN-2.95.o
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111 0 0 111 6f switch-CHAIN-3.3.o
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95 0 0 95 5f switch-CHAIN-3.4.o
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95 0 0 95 5f switch-CHAIN-4.0.o
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95 0 0 95 5f switch-CHAIN-4.1.o
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95 0 0 95 5f switch-CHAIN-4.2.orig-HEAD.o
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95 0 0 95 5f switch-CHAIN-4.3-HEAD.o
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95 0 0 95 5f switch-CHAIN-4.3.orig-HEAD.o
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Content-Type: text/x-diff; charset=us-ascii
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Content-Disposition: attachment; filename="gcc-4.3.gcc-flatten-switch-stmt.00.diff"
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Index: gcc-4.2.0/gcc/stmt.c
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===================================================================
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--- gcc-4.2.0.orig/gcc/stmt.c (revision 123843)
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+++ gcc-4.2.0/gcc/stmt.c (working copy)
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@@ -2517,7 +2517,11 @@ expand_case (tree exp)
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use_cost_table
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= (TREE_CODE (orig_type) != ENUMERAL_TYPE
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&& estimate_case_costs (case_list));
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- balance_case_nodes (&case_list, NULL);
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+ /* When optimizing for size, we want a straight list to avoid
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+ jumps as much as possible. This basically creates an if-else
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+ chain. */
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+ if (!optimize_size)
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+ balance_case_nodes (&case_list, NULL);
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emit_case_nodes (index, case_list, default_label, index_type);
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emit_jump (default_label);
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}
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@@ -3075,6 +3079,7 @@ emit_case_nodes (rtx index, case_node_pt
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{
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if (!node_has_low_bound (node, index_type))
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{
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+ if (!optimize_size) /* don't jl to the .default_label. */
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emit_cmp_and_jump_insns (index,
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convert_modes
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(mode, imode,
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Content-Type: text/x-csrc; charset=us-ascii
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Content-Disposition: attachment; filename="switch.c"
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int
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commutative_tree_code (int code)
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{
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#define CASE(val, ret) case val:/* __asm__("# val="#val ",ret="#ret);*/ return ret;
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#ifndef CHAIN
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switch (code)
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{
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# if 1
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CASE(1,3)
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CASE(3,2)
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CASE(5,8)
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CASE(7,1)
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CASE(33,4)
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CASE(44,9)
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CASE(55,10)
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CASE(66,-1)
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CASE(77,99)
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CASE(666,0)
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# else
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case 1:
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return 3;
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case 3:
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return 2;
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case 5:
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return 8;
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case 7:
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return 1;
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case 33:
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return 4;
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case 44:
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return 9;
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case 55:
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return 10;
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case 66:
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return -1;
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case 77:
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return 99;
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case 666:
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return 0;
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# endif
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default:
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break;
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}
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return 4711;
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#else
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if (code == 1)
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return 3;
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else if (code == 3)
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return 2;
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else if (code == 5)
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return 8;
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else if (code == 7)
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return 1;
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else if (code == 33)
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return 4;
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else if (code == 44)
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return 9;
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else if (code == 55)
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return 10;
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else if (code == 66)
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return -1;
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else if (code == 77)
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return 99;
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else if (code == 666)
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return 0;
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else
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return 4711;
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#endif
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}
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--AhhlLboLdkugWU4S--
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